Iterator collection, iterator

Iterator collection, iterator

Package com. starain. Iterator;
/* The shortcut for code sorting is Ctrl + Shift + F.
* Enter the shortcut key main character + Alt +/in the main method/
* Output shortcut key: sysout character + Alt + /*/

Import java. util. *; // two commonly used packages, java. lang Language Pack and java. util practical package
/* Java. lang is automatically introduced,
* Contains data packages (Byte, Short, Integer, Long, Float, Double, Character, Boolean ),
* String class (constant String, variable StringBuffer, StringBuilder)
* Math for mathematics,
* System and Runtime class (System, Runtime ),
* Class operation Class (Class, ClassLoader)
* Manual introduction of java. util
* Date, Calendar, GregorianCalendar)
* GregorianCalendar cal = (GregorianCalendar) GregorianCalendar. getInstance ();
* Cal. isLeapYear (year); returns the boolean Type and determines whether it is a leap year.
* Collection class (Collection -- Set -- HashSet, TreeSet;
* Collection -- List -- ArrayList, Vector, sorted List;
* Map -- HashTable, HashMap, WeakHashMap)
**/

Public class IteratorDemo1 {
Public static void main (String [] args ){
/* List is an ordered set in the original order, which can be repeated.
* ArrayList asynchronous mode, high performance, but thread security
* Vector is a synchronization mode with low performance, but thread security */
List <String> list1 = new ArrayList <String> (); // List is an interface and cannot be directly instantiated. The generic type and subclass instantiation method are used.

/* Add operation */
List1.add ("my ");
List1.add ("name ");
List1.add ("is ");
List1.add ("starain ");

/* Determine whether the operation is null */
Boolean bool1 = list1.isEmpty ();

If (! Bool1 ){

/* Output as an array all day */
System. out. println (list1 );

/* Enhanced for loop printing mode */
For (String str: list1 ){
System. out. print (str + "");
}

System. out. println ("\ n =================== ");
System. out. print ("two gorgeous split lines ");
System. out. println ("\ n =================== ");

/* Iterator interface Printing Output Mode
* The standard form of set output is the Iterator interface.
* Principle: Iterator is a specialized iterative output interface. It identifies the elements one by one to determine whether there is any content. If there is any content, it extracts the content */
Iterator <String> iterator1 = list1.iterator ();
While (iterator1.hasNext ()){
System. out. print (iterator1.next () + "");
}

/* Remove operation */
List1.remove ("is ");

System. out. println ();
For (String str2: list1 ){
System. out. print (str2 + "");
}
}

System. out. println ("\ n =================== ");
System. out. print ("two gorgeous split lines ");
System. out. println ("\ n =================== ");

/* Set is a Set that does not repeat, and does not allow repetition. If it is repeated, It is overwritten before
* HashSet unordered (non-original)
* Automatic TreeSet sorting. Based on Map, an error is returned when the sorting cannot be completed */
Set <String> set1 = new HashSet <String> ();
Set <String> set2 = new TreeSet <String> ();

/* Add an element to HashSet set1 */
Set1.add ("A"); // copy and paste the shortcut key Ctrl + Alt + downward key
Set1.add ("B ");
Set1.add ("B ");
Set1.add ("D ");
Set1.add ("C ");
Set1.add ("E ");
Set1.add ("F ");
Set1.add ("C ");
Set1.add ("G ");

/* Output */
System. out. println (set1 );

/* Add elements to TreeSet set2 */
Set2.add ("A"); // copy and paste the shortcut key Ctrl + Alt + downward key
Set2.add ("B ");
Set2.add ("B ");
Set2.add ("D ");
Set2.add ("C ");
Set2.add ("E ");
Set2.add ("F ");
Set2.add ("C ");
Set2.add ("G ");

/* Output */
System. out. println (set2 );


/* Map example
* The storage format of the Map interface is key-> value. For example, the address book uses the name key to locate the corresponding phone number value.
* Map <K, V> two generics, corresponding to key and value */
Map <String, String> map1 = new HashMap <String, String> ();

/* Map is added as the put () method */
Map1.put ("key1", "www ");
Map1.put ("key2 ",".");
Map1.put ("key3", "starain ");
Map1.put ("key4 ",".");
Map1.put ("key5", "index ");
Map1.put ("key6 ",".");
Map1.put ("key7", "com ");

/* Determine the memory first
* Determine whether the value is containKey (key) by using the key)
* Use value to determine containValue (value )*/
Boolean boolkey1 = map1.containsKey ("key1 ");
Boolean boolkey2 = map1.containsKey ("key99 ");
If (boolkey1 ){

/* Print value through key */
String str1 = map1.get ("key1 ");
System. out. println (str1 );
} Else System. out. println ("key1 does not exist ");
If (boolkey2 ){
String str99 = map1.get ("key99 ");
System. out. println (str99 );
} Else System. out. println ("key99 does not exist ");


/* Iterator interface printing */

/* Print the key */
Set <String> s = map1.keySet (); // the return value of keySet () is Set.
Iterator <String> i1 = s. iterator ();
While (i1.hasNext ()){
System. out. print (i1.next () + ""); // The remove operation on the collection is prohibited in the action.
}

System. out. println ("\ n =================== ");
System. out. print ("two gorgeous split lines ");
System. out. println ("\ n =================== ");

/* Print value */
Collection <String> c = map1.values (); // value () returns the Collection type.
Iterator <String> i2 = c. iterator ();
While (i2.hasNext ()){
System. out. print (i2.next () + "");
}
}
}